drm: rcar-du: Allow importing non-contiguous dma-buf with VSP

On R-Car Gen3, the DU uses a separate IP core named VSP to perform DMA
from memory and composition of planes. The DU hardware then only handles
the video timings and the interface with the encoders. This differs from
Gen2, where the DU included a composer with DMA engines.

When sourcing from the VSP, the DU hardware performs no memory access,
and thus has no requirements on imported dma-buf memory types. The GEM
CMA helpers however still create a DMA mapping to the DU device, which
isn't used. The mapping to the VSP is done when processing the atomic
commits, in the plane .prepare_fb() handler.

When the system uses an IOMMU, the VSP device is attached to it, which
enables the VSP to use non physically contiguous memory. The DU, as it
performs no memory access, isn't connected to the IOMMU. The GEM CMA
drm_gem_cma_prime_import_sg_table() helper will in that case fail to map
non-contiguous imported dma-bufs, as the DMA mapping to the DU device
will have multiple entries in its sgtable. The prevents using non
physically contiguous memory for display.

The DRM PRIME and GEM CMA helpers are designed to create the sgtable
when the dma-buf is imported. By default, the device referenced by the
drm_device is used to create the dma-buf attachment. Drivers can use a
different device by using the drm_gem_prime_import_dev() function. While
the DU has access to the VSP device, this won't help here, as different
CRTCs use different VSP instances, connected to different IOMMU
channels. The driver doesn't know at import time which CRTC a GEM object
will be used, and thus can't select the right VSP device to pass to
drm_gem_prime_import_dev().

To support non-contiguous memory, implement a custom
.gem_prime_import_sg_table() operation that accepts all imported dma-buf
regardless of the number of scatterlist entries. The sgtable will be
mapped to the VSP at .prepare_fb() time, which will reject the
framebuffer if the VSP isn't connected to an IOMMU.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_drv.c

@@ -529,7 +529,11 @@ DEFINE_DRM_GEM_CMA_FOPS(rcar_du_fops);
 
 static const struct drm_driver rcar_du_driver = {
 	.driver_features	= DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
-	DRM_GEM_CMA_DRIVER_OPS_WITH_DUMB_CREATE(rcar_du_dumb_create),
+	.dumb_create		= rcar_du_dumb_create,
+	.prime_handle_to_fd	= drm_gem_prime_handle_to_fd,
+	.prime_fd_to_handle	= drm_gem_prime_fd_to_handle,
+	.gem_prime_import_sg_table = rcar_du_gem_prime_import_sg_table,
+	.gem_prime_mmap		= drm_gem_prime_mmap,
 	.fops			= &rcar_du_fops,
 	.name			= "rcar-du",
 	.desc			= "Renesas R-Car Display Unit",

drivers/gpu/drm/rcar-du/rcar_du_kms.c

@@ -19,6 +19,7 @@
 #include <drm/drm_vblank.h>
 
 #include <linux/device.h>
+#include <linux/dma-buf.h>
 #include <linux/of_graph.h>
 #include <linux/of_platform.h>
 #include <linux/wait.h>
@@ -325,6 +326,51 @@ const struct rcar_du_format_info *rcar_du_format_info(u32 fourcc)
  * Frame buffer
  */
 
+static const struct drm_gem_object_funcs rcar_du_gem_funcs = {
+	.free = drm_gem_cma_free_object,
+	.print_info = drm_gem_cma_print_info,
+	.get_sg_table = drm_gem_cma_get_sg_table,
+	.vmap = drm_gem_cma_vmap,
+	.mmap = drm_gem_cma_mmap,
+	.vm_ops = &drm_gem_cma_vm_ops,
+};
+
+struct drm_gem_object *rcar_du_gem_prime_import_sg_table(struct drm_device *dev,
+				struct dma_buf_attachment *attach,
+				struct sg_table *sgt)
+{
+	struct rcar_du_device *rcdu = to_rcar_du_device(dev);
+	struct drm_gem_cma_object *cma_obj;
+	struct drm_gem_object *gem_obj;
+	int ret;
+
+	if (!rcar_du_has(rcdu, RCAR_DU_FEATURE_VSP1_SOURCE))
+		return drm_gem_cma_prime_import_sg_table(dev, attach, sgt);
+
+	/* Create a CMA GEM buffer. */
+	cma_obj = kzalloc(sizeof(*cma_obj), GFP_KERNEL);
+	if (!cma_obj)
+		return ERR_PTR(-ENOMEM);
+
+	gem_obj = &cma_obj->base;
+	gem_obj->funcs = &rcar_du_gem_funcs;
+
+	drm_gem_private_object_init(dev, gem_obj, attach->dmabuf->size);
+	cma_obj->map_noncoherent = false;
+
+	ret = drm_gem_create_mmap_offset(gem_obj);
+	if (ret) {
+		drm_gem_object_release(gem_obj);
+		kfree(cma_obj);
+		return ERR_PTR(ret);
+	}
+
+	cma_obj->paddr = 0;
+	cma_obj->sgt = sgt;
+
+	return gem_obj;
+}
+
 int rcar_du_dumb_create(struct drm_file *file, struct drm_device *dev,
 			struct drm_mode_create_dumb *args)
 {

drivers/gpu/drm/rcar-du/rcar_du_kms.h

@@ -12,10 +12,13 @@
 
 #include <linux/types.h>
 
+struct dma_buf_attachment;
 struct drm_file;
 struct drm_device;
+struct drm_gem_object;
 struct drm_mode_create_dumb;
 struct rcar_du_device;
+struct sg_table;
 
 struct rcar_du_format_info {
 	u32 fourcc;
@@ -34,4 +37,8 @@ int rcar_du_modeset_init(struct rcar_du_device *rcdu);
 int rcar_du_dumb_create(struct drm_file *file, struct drm_device *dev,
 			struct drm_mode_create_dumb *args);
 
+struct drm_gem_object *rcar_du_gem_prime_import_sg_table(struct drm_device *dev,
+				struct dma_buf_attachment *attach,
+				struct sg_table *sgt);
+
 #endif /* __RCAR_DU_KMS_H__ */

drivers/gpu/drm/rcar-du/rcar_du_vsp.c

@@ -187,17 +187,43 @@ int rcar_du_vsp_map_fb(struct rcar_du_vsp *vsp, struct drm_framebuffer *fb,
 		       struct sg_table sg_tables[3])
 {
 	struct rcar_du_device *rcdu = vsp->dev;
-	unsigned int i;
+	unsigned int i, j;
 	int ret;
 
 	for (i = 0; i < fb->format->num_planes; ++i) {
 		struct drm_gem_cma_object *gem = drm_fb_cma_get_gem_obj(fb, i);
 		struct sg_table *sgt = &sg_tables[i];
 
-		ret = dma_get_sgtable(rcdu->dev, sgt, gem->vaddr, gem->paddr,
-				      gem->base.size);
+		if (gem->sgt) {
+			struct scatterlist *src;
+			struct scatterlist *dst;
+
+			/*
+			 * If the GEM buffer has a scatter gather table, it has
+			 * been imported from a dma-buf and has no physical
+			 * address as it might not be physically contiguous.
+			 * Copy the original scatter gather table to map it to
+			 * the VSP.
+			 */
+			ret = sg_alloc_table(sgt, gem->sgt->orig_nents,
+					     GFP_KERNEL);
+			if (ret)
+				goto fail;
+
+			src = gem->sgt->sgl;
+			dst = sgt->sgl;
+			for (j = 0; j < gem->sgt->orig_nents; ++j) {
+				sg_set_page(dst, sg_page(src), src->length,
+					    src->offset);
+				src = sg_next(src);
+				dst = sg_next(dst);
+			}
+		} else {
+			ret = dma_get_sgtable(rcdu->dev, sgt, gem->vaddr,
+					      gem->paddr, gem->base.size);
 			if (ret)
 				goto fail;
+		}
 
 		ret = vsp1_du_map_sg(vsp->vsp, sgt);
 		if (ret) {